The identification of critical regulatory sequences and the subsequent characterization of cognate transcription factors is of seminal importance because it provides information of the fundamental mechanisms that regulate spatial and developmental gene expression in vivo. Our laboratory is interested in the mechanisms that signal genes to become and remain active in some tissues, such as liver, and to linger silent in others. We are particularly interested in the role that two members of the C/EBP family, C/EBPalpha and C/EBPepsilon, play during cell proliferation and differentiation of hepatocytes, adipocytes and hematopoietic cells respectively. Our approach is to study the (i) the functional roles of the C/EBPalpha and C/EBPepsilon molecules during mouse development using homologous recombination for targeted interruption of both genes (ii) biochemical structure/function studies of C/EBPepsilon (iii) development of potent semi-synthetic cell-specific transcriptional elements for use in targeted transcriptional gene therapy strategies. The other major focus of our laboratory is the development of novel vectors for cancer gene immunotherapy. Results from studies where genetically engineered tumor cells armed with cytokine genes to mount tumor-specific immune response have been promising. This type of approach has strong potential clinical applications because it may facilitate the use of therapeutic vaccines for the treatment of tumors. To this end, different cancer gene therapy approaches have been undertaken using adoptive immunotherapy and to utilize cytokine gene modified tumor cells as vaccines for treatment of cancer. Amid the elegance of these approaches, the results have been hampered by low levels of expression of the cytokines. Recent studies from this branch (R. M. Blaese) indicate that conditionally toxic genes (HSV-TK) followed by antiviral drug administration have both great toxic effects and involve an immune component in the mechanisms of rejection of the tumor. It is our goal to generate a combined approach which may eventually have high potential therapeutic value for several human cancers. This strategy is based on (i) highly efficient autocatalytic expression vectors derived from alphaviruses, e.g. Semliki Forest Virus (SFV) and (ii) hybrid Adenoviral /SFV chimeric vectors. Initial results demonstrated that transcriptional units of SFV can be incorporated into the Adenoviral backbone, making it possible to test the potential synergistic anti-tumor effects of a combination of cytokine and HSV-TK.